With the ever-increasing popularity of high dynamic range (HDR) display, the backlight unit (BLU) of a liquid crystal display (LCD) must be designed to meet the requirements on the wide color gamut operation. Nowadays, a possible way to attain a wide color gamut for display is to use the quantum dot structure. The quantum dot display typically consists of a quantum dot tube and a quantum dot film.
The quantum dot tube is disposed adjacently to the light source. However, the temperature in the ambience of the light source is quite high. Considering the issue of reliability, it would be advantageous to dispose the quantum dot film in the backlight film structure. The most common way to design a wide color gamut display is to dispose a blue-light light-emitting diode (LED) in conjunction with a quantum dot film to emit white light, along with the color filter of the LCD panel to form a wide color gamut space. It is known that quantum dot material is a photoluminescent material, which means that blue light must shine the surface of the quantum dot material to allow the quantum dot material to absorb the blue light, so as to emit red light and green light. For the contemporary direct backlight unit and edge backlight unit, the light emitted from LED directly hits the LCD panel through the quantum dot film, which would in turn cause a low utilization of the quantum got material of the quantum dot film.
A commonly-used approach to enhance the utilization of the quantum dot material is to dispose a quantum dot film at a position nearest to the light source in the backlight film structure, and coat the quantum dot film with two brightness enhancement films (or prism films). A diffuser film may be added so that light can be emitted from the quantum dot film and hits the brightness enhancement films and the diffuser film disposed above. Meanwhile, a part of the light is transmitted therethrough and a part of the light is reflected. The reflected light re-enters the quantum dot film to excite the quantum dot material to emit red light and green light, thereby increasing the excitation efficiency of the quantum dot material. However, this would require the quantum dot film to cooperate with the brightness enhancement films and the diffuser film for enhancing its excitation efficiency. If this approach is applied, the excitation efficiency of the quantum dot film is still too low to excite sufficient amount of red light and green light. Under this condition, the backlight provided for the LCD panel would be represented with blue tone, and the brightness of the LCD is quite low.